This invention relates to apparatus for generating a three-dimensional display from a conventional television screen or computer monitor, and in particular to an adapter that may be placed in front of a television screen or computer monitor to enable three-dimensional images to be perceived by a viewer.
When a viewer looks at a scene, the left and right eyes will each receive a different left and right image. Corresponding points between the two images are locally displaced from each other by an amount commonly known as the disparity that is dependent on the distance between the point and the viewer. Based on this principle, stereoscopic three-dimensional images can be generated if it is possible to direct left and right images to the left and right eyes. By controlling the disparity between corresponding points a sense of depth can be created.
Developing a system that allows a two-dimensional screen, for example a television screen or a computer monitor, to display an image that may be perceived by a viewer as a three-dimensional image has been a long sought after goal and a number of prior proposals exist. A number of existing techniques and proposals are summarized as follows.
U.S. Pat. No. 3,737,567 and 3,621,127 disclose systems in which the left and right images are recorded in the odd and even (or vice versa) fields of an interlaced video signal. The viewer then wears spectacles consisting of two LCD shutters that are opened and closed in a complementary manner so that when the field containing the left image is displayed on the screen the left shutter is open and the other closed, while when the field containing the right image is displayed, the right shutter is open and the left is closed. This ensures that only the left eye sees the left image, and only the right eye sees the right image. The opening and closing of the two shutters is synchronized with the field repetition frequency.
U.S. Pat. No. 4,281,341 describes an alternative approach in which an onscreen modulator is applied to polarize video frame images into orthogonal phases. The left and right images are perceived by the left and right eyes respectively by the viewer wearing orthogonally polarised glasses.
These proposals ensure that the left and right eyes see only the left and right images respectively and thus allow three-dimensional images to be generated. However, in both these processes a device is needed to extract the field synchronization signal from the video signal and to control the LCD shutters or the onscreen modulator. The synchronization signal may be derived from the video signal, but in general terms the field synchronization signal is not externally available in a conventional television set. Furthermore, where LCD shutters are used, a circuit is required in the viewer""s spectacles to control the on/off action of the LCD shutters. These technical requirements reduce the practicality of these approaches.
Another approach to providing a three-dimensional effect is to impose three-dimensional perception on the human visual system using the Pulfrich effect. In methods based on this approach, the left and right eyes view the screen through two light filters of a considerable difference in opaqueness.
An apparatus for generating a three-dimensional image in accordance with the principles of the present invention includes polarization means adapted to be placed in front of a screen for displaying images, and means for controlling the polarization of said polarization means in accordance with the nature of the images displayed on said screen.
The polarization means may be a liquid crystal polarizer having a polarization angle that depends on an applied voltage.
The control means may include a control region of the screen.
The apparatus may include a light sensitive means that is adapted to face the control region, the control region being adapted to produce differing light patterns. The light sensitive means may generate an output control signal that controls the voltage applied to said liquid crystal polarizer.
The apparatus may further include spectacles for viewing the image output, the spectacles having left and right lenses that are orthogonally polarized.
The apparatus may be capable of generating stereoscopic three-dimensional images and Pulfrich three-dimensional images.
A method for generating three-dimensional images from a two-dimensional screen in accordance with the principles of the present invention includes the steps of: displaying a two-dimensional image on a screen, passing the image through a polarizer, and viewing the polarized image through a pair of spectacles having orthogonally polarized lenses.
The polarization angle of the polarizer may be variable depending on the type of three-dimensional image to be generated. The polarization angle of the polarizer may be varied by a control region forming, part of the two-dimensional image. The polarizer may be a liquid crystal polarizer, so that the polarization angle is varied by varying an applied voltage.
The control region may include an illumination pattern wherein the applied voltage is varied by means of a control signal generated by a light sensitive element that senses the illumination pattern.
The two-dimensional image may have a plurality of sequential frames, the frames being alternately left and right images, wherein the polarization angle of the polarizer is varied in synchrony with the alternating images. The left and right images may be differently polarized such that the left images can be viewed only through the left lens of the viewing spectacles, and the right images can bep viewed only through the right lens of the viewing spectacles so as to generate a stereoscopic three-dimensional image.
The two-dimensional image may have a plurality of odd and even fields, the polarization angle being held constant in both the odd and even fields. The image may polarized such that the light intensity viewed through one of the lenses is greater than the light intensity viewed through another of lenses, so as to generate a Pulfrich phenomenon.
The two-dimensional image may have a plurality of odd and even fields, the polarization angle being held constant in both the odd and even fields. The image may be polarized such that the light intensity viewed through one of the lenses is the same as the light intensity viewed through another of the lenses, so as to generate a conventional two-dimensional image.